Wrapping pipe to prevent corrosion and wear has been well known since the 1940's. The method established at that time has changed little, although the materials used to make the wrap and bond it to the pipe have improved. The abilities of these products to perform satisfactorily have been almost universally dependent upon applying a solvent based primer directly on to the properly cleaned pipe surface prior to application of the hot or cold-applied tapes, shrink sleeves or other pipe-line coatings. The solvent based primers used for coating the pipe surface consist of some combination of organic solvent with elastomeric/resin based solid materials dissolved therein. The solvents act as a vehicle to carry the solids for deposition on the pipe surface. The solvent evaporates after application to produce a dry but flexible solid coating on the pipe surface. This "primer coating" then acts to enhance all of the vital functions of the tape, shrink sleeve or coating adhesive bonding systems.
Most, if not all, corrosion engineers believe the premise that to properly protect pipes from corrosion, application of the proper primer before the application of pipeline coatings is essential. It was generally believed that the solvent portion of the solvent based primer was necessary to achieve a wetting/bonding action on the cleaned pipe surface, which caused the solids portion of the solvent based primer to bond effectively to the pipe, thus enhancing the bonding of the adhesive bonding surface of the tapes or shrink sleeves. The belief in the industry was that a wet primer application is an integral part of the total tape or shrink sleeve wrapping system. Thus, the result obtained from the current invention, elimination of the primer, was unexpected and highly desirable.
Application of tape, shrink sleeve or wrap in the conventional manner was complicated and labor intensive. First, the pipe to be wrapped had to be thoroughly cleaned. Next, a solvent based primer was manually applied to the pipe, and the solvent was allowed to evaporate into the environment. Third, the wrap, including the adhesive, was applied to the pipe. This process created several difficulties.
First, the individual applying the primer must decide how much to use. Too little primer did not generate the strength of bond necessary and gave poor results. Too much primer wasted material, increased costs and also gave poor results. It was necessary to spend time training the individual doing the application of the primer to get the best results.
Second, it was necessary to match the primer with the adhesive on the wrap. Not all primers matched up correctly with any adhesive, and a mismatch would result in a complete failure to adhere to the pipe.
Third, the process of applying the primer was labor intensive. The person making the application must do the job manually, usually with a brush.
Fourth, the primer was environmentally unsound. The primers were typically composed of 75-85% solvents, and 15-25% solids. Many of the primers were highly flammable due to the high solvent content, and furthermore, some were toxic and/or carcinogenic. After the primer was applied, the solvent was allowed to evaporate into the environment, leaving the solids behind. The wrap with the adhesive was then applied on top of the remaining solids that coated the pipe. However, many tons of solvent evaporated into the environment during this process. These solvents included methyl ethyl ketone, toluene and xylene.
Many efforts have been made to eliminate primers. One such effort revolves around the use of epoxy resins applied to the surface of the pipe before applying the wrap to the pipe. Epoxy resin treatment suffers from many problems, including high cost, the toxicity of the amines used in the process, the limited pot life of the amines, the long curing times involved and temperature restrictions. For example, epoxy resins usually take an hour to cure, and thus the wrap cannot be applied for this length of time. The resins cannot be applied below 50.degree. F. Thus, epoxy resins suffer from high costs, use limitations and risks of environmental danger that make it impractical to use.
Other efforts have failed to produce the proper results. When a wrap is tested, the standard test is the cathodic disbondment test, ASTM G-8. In the cathodic disbondment test, a 1/4" hole is drilled through the outer wrap and the pipe, the pipe is then immersed in a 3% salt solution, and a 1.5 V current is impressed on the pipe. The amount of disbondment is then measured after 30 days in this environment. Prior efforts to make a primerless wrap have failed to give results about the same as those results achieved by the old method of applying the primer and then the wrap. The inventors of the primerless tape or shrink sleeve of this application increased the severity of the test by running the voltage at 3 V for 60 days to be sure it was equal to or better than primer applied tape.
Under the harsher conditions utilized by the inventors, with neither a primer nor the solids material used, the amount of disbondment ranges from 7 to 8 square inches. When primer or the solids material of the instant invention are used, the amount of disbondment is usually well under 2 square inches, but anything under 3 square inches is considered acceptable.
Still other efforts to create a primerless wrap have failed from the very beginning. Early efforts at generating a primerless wrap included simply evaporating the solvents from the primer, and then attempting to apply the solids remaining to the wrap plus the adhesive. These efforts failed because the viscosity of the remaining solids was too high; the solids set up and did not flow. Furthermore, even when the remaining solids were forced onto the wrap plus the adhesive, the mixture failed the cathodic disbondment test.
Other wraps require application with heat, and did not provide the same excellent results in the cathodic disbondment tests as the current invention. The inventors of the primerless tape of this application initially attempted to create a hot melt, using temperature to overcome the viscosity problems, and apply the hot melt to the wrap plus adhesive. These efforts failed to overcome the viscosity problems, and the inventors were forced to try different materials to achieve a blend with the viscosity desired.